1. Field of the Invention
This invention relates to a device for the changing of the wavelength of light that is suitable for use in, for example, information processing devices that make use of laser light, apparatus for measurement with the use of light, and the like. More particularly, this invention relates to a device for shortening the wavelength of light. This shortening of the wavelength of the laser light used in, for example, optical disk systems, laser beam printers, and other such devices that make use of laser light, can result in higher performance.
2. Description of the Prior Art
In recent years, devices for information processing and the like that make use of semiconductor lasers, such as optical disk systems and laser beam printers, have been put into practical use. The laser light that is used in such systems as a light source has an oscillating wavelength of, for example, 780 .mu.m or 830 .mu.m. There is a proportional relationship between the wavelength of the laser light and the diameter of the light-focusing spot (the minimum light-focusing diameter), and the shorter the wavelength of laser light, the smaller the diameter of the light-focusing spot. The smaller the diameter of the light-focusing spot, the more possible becomes the increase in the recording density of, for example, an optical disk of an optical disk system, so that a laser beam printer can achieve greater resolution. Also, in the field of measurement with the use of light such as interference measurement and the like, the use of short wavelengths of laser light can increase the accuracy of the results of measurement. In such ways, the performance of devices that make use of laser light can be improved by the use of a device for the shortening of the oscillation wavelength of this light.
By the use of an InGaAlP system for the material of the semiconductor laser, it has been found experimentally that it is possible to obtain laser light with a wavelength in the region of 600 .mu.m, but there are still a number of problems that remain concerning reliability and the like that must be solved before this is put into practical use. Also, at the present, materials for semiconductors that will give laser light of yet shorter wavelengths are not known.
Devices for the changing of the wavelength of light, i.e., the shortening of the wavelength of laser light, in general, produce a harmonic component with a wavelength of .lambda./n, wherein .lambda. is the wavelength of laser light that is incident upon the said devices and n is an integer (e.g., 2, 4, 6, . . . or 3, 6, 9, . . . ). At present, with the use of a YAG (yttrium-aluminium-garnet) laser with a wavelength of 1.06 .mu.m, it is possible to produce laser light with a wavelength of 0.53 .mu.m for green laser light, and with the use of a semiconductor laser with a wavelength of 0.83 .mu.m, it is possible to produce laser light with a wavelength of 0.415 .mu.m for blue laser light.
FIG. 6 shows a conventional device 10 for the changing of the wavelength of light, which has a non-linear optical crystal 1 such as the Z plate of crystals of LiN.sub.b O.sub.3 in which the direction of arrow A in FIG. 6 is in the direction of the crystal axis Z. In the upper portion of the non-linear optical crystal 1 shown in FIG. 6, an optical waveguide 2 with a width, for example, of 2 .mu.m and a depth of 0.55 .mu.m is formed from one side surface of the non-linear optical crystal 1 to the other side surface thereof by the proton exchange method or the like so as to be parallel with, for example, crystal axis Y.
In device 10 for the changing of the wavelength of light, for example, laser light 3 from a YAG laser or the like with a wavelength of 1.06 .mu.m is fed into one facet of the optical waveguide 2 and proceeds along the inside of the optical waveguide 2. At this time, because the non-linear optical coefficient of the non-linear optical crystal 1 is large, a harmonic light 4 with a wavelength that is 1/2 of the wavelength of the laser light 3 (0.53 .mu.m) is radiated inside of the non-linear optical crystal 1 at an angle .theta. that satisfies the phase matching conditions.
When YAG laser light (with a wavelength of 1.06 .mu.m) is fed into LiN.sub.b O.sub.3 crystals, the harmonic light 4 is radiated at a 12.5.degree. angle from the direction in which the YAG laser light is proceeding. This harmonic light 4, as shown in FIG. 6, is radiated along the entire region of the optical waveguide 2, and radiated out from the device 10 for the changing of the wavelength of light.
The harmonic component 4 is produced with an intensity in proportion to the second power of the intensity of the laser light that is fed in the device 10. For this reason, at the vicinity of the surface of the optical waveguide 2 into which the laser light is fed, the efficiency of the change from the long wavelength light into the harmonic light 4 is high and the laser light decays as it proceeds along the optical waveguide 2, resulting in a decrease in the efficiency of the change and a decrease in the intensity of the harmonic light 4. Moreover, because the harmonic light 4 is output from the narrow optical waveguide 2, diffraction causes the harmonic light 4 to expand in the direction of the width of the optical waveguide 2.
Therefore, the harmonic light 4 that is output takes on a narrow, long oval shape, and its intensity also is not uniform. This kind of light beam in an oval shape of non-uniform intensity is not suitable for use as a light source in optical disk apparatuses or laser printers. Moreover, because there is a fractional angle (of 12.5.degree.) between the direction of the feeding in of laser light and the output of the harmonic light 4, the construction of a system with this kind of device 10 for the changing of the wavelength of light is complex.
In the conventional device 10 for the changing of the wavelength of light, the problems mentioned above limit the field of applications.